Because there is a bigger picture here than just "buy a different phone" as mobile computing becomes more ubiquitous. I think that having a single app store on the dominant platform that everyone is forced to go through is akin to having a single browser on the dominant OS. So in the end it's not about suing Apple per se but if a suit against Apple were successful then the rest of the market players would be forced to open up as well.
Android is more open in the sense that there is more than one market and anyone can build a marketplace for apps. Yes, there are places where Google is not open with Android as well but my main problem is there is only one app store for iDevices. My thinking is that if Apple is forced to open up in terms of allowing more than one channel to sell apps through, or to sell directly, that it won't cede the market to Google but will set a precedent for all players.
It sounds like you are saying that you want Apple to be forced to do what Google has already done. Doesn't this mean the the precedent has already been set but Google?
That leads back to the original question: Why is it so important for Apple to be forced to operate like Android when people are free to just buy an Android phone if they want that kind of environment?
2) Carriers (AT&T) are known for disabling app sideloading.
3) Having to root your device presents the basic user with a major technical hurdle, and in some cases, an outright impossibility.
If you're going to advocate as an alternative an entire platform you can't guarantee freedom on, for freedom's sake, why advocate it?